SYNTHESIS OF SARCOSINATE SURFACTANTS

Abstract: A method for preparing sarcosinate amido acids and salts thereof of formula (IA) wherein R is a C1 or higher hydrocarbyl substituent, and M is a cationic moiety selected from alkali metal salts and hydrogen, comprising the steps of (a) reacting under anhydrous conditions, in the presence of a base catalyst with basicity equal to or greater than alkoxide catalyst, a carboxylic acid ester of formula (II) with a sarcosine amino acid salt of structure (B) wherein R is as described before, R<1> is a C1 or higher hydrocarbyl substituent, and M is an alkali metal salt; and (b) optionally, neutralizing the sarcosinate amido acid salt formed by step (a) to form the sarcosinate amido acid, whereby M is hydrogen in formula (IA).

Description: SYNTHESIS OF SARCOSINATE SURFACTANTS This is a continuation-in-part application of pending application U.S. Serial Number 08/121,007, filed September 14, 1993. FIELD OF THE INVENTION The present invention relates to the chemical synthesis of sarcosinate compounds useful as surfactants. BACKGROUND OF THE INVENTION The synthesis of ingredients for use in low unit cost consumer goods such as laundry detergents, fabric softeners, hard surface cleansers, and the like, is of considerable interest to manufacturers. Indeed, while formularies and patents are filled with listings of prospective ingredients for use in such products, the reality is that many such ingredients are simply too expensive for day-to-day use. This expense is often due either to the cost of the raw materials used to make such ingredients, or to the complex reaction and processing chemistry which is required in their manufacture. Accordingly, manufacturers have conducted a continuing search for both inexpensive raw materials and simple reaction sequences which can produce high performance, high value ingredients at the lowest possible cost. The amido acids comprise one class of chemicals whose amido and carboxylate functional groups suggest their use as surfactants (e.g., sarcosinates), fabric softeners, antistatic agents and the like. Moreover, the amido acids constitute a basic raw material for the amido phenyl ester sulfonate class of chemicals which can serve as bleach activators in laundry detergents and other types of bleach-containing cleaning compositions. On the positive side, the amido acids and their aforementioned derivatives are potentially obtainable from inexpensive raw materials. Unfortunately, the synthesis of certain amido acids is somewhat complicated and can involve the use of solvents, with additional problems associated with recycle streams and the like. Problems can also arise with the formation of undesirable colored by-products. The present invention provides a simple method for the synthesis of sarcosinate amido acids. The individual reaction sequences herein proceed in acceptable yields (typically 80%, and higher) and, importantly, result in products with minimal discoloration. In some cases, the reactions may be conducted without added solvents, i.e., the reactants or products act as solvents. Hence, for many purposes the reaction products need not be extensively purified which further improves the overall economics of the processes. BACKGROUND ART See Surfactant Science Series. Vol. 7. Part HI, p581-617, for general syntheses of amido acids. See Kiyoshi Matsumoto, Shiro Hashimoto, and Shinichi Otani, Angew. Chem. Int. Ed. Engl., 25(6), p565-566 ( 1986) for review of syntheses of amides from esters and amines. See Richard J. De Feoand and Paul D. Strickler, L Org. Chem.. 28. p2915-2917 (1963) for general statement that secondary amines do not react with esters to form amides. See also U.S. Patent 3,836,551, to Schroeder et al., for salts of N-acylamino carboxylic acids said to be made by reacting an amino acid and a carboxylic acid, ester, or amide at 100° C - 250° C in the presence of a salt-forming basic compound such as an alkali metal or alkaline earth metal hydroxide, a tertiary amine, or a quaternary ammonium hydroxide. SUMMARY OF THE INVENTION The present invention encompasses a method for preparing amido acids and salts thereof of the formula (IA) wherein R is a C, or higher hydrocarbyl substituent, and M is a cationic moiety selected from alkali metal salts and hydrogen, by the steps of: (a) reacting under anhydrous conditions, in the presence of a base catalyst with basicity equal to or greater than alkoxide catalyst, a carboxylic acid ester of the formula O II R-C-OR1 with a sarcosine salt of the structure CHs H-N-CH2-CO2M wherein R is as described before, R^ is a C, or higher hydrocarbyl substituent (preferably methyl, ethyl, propyl, or butyl), and M is an alkali metal salt; and (b) optionally, neutralizing the salt formed by step (a) to form the sarcosinate amido acid, whereby M is hydrogen in Formula IA. The preferred method for preparing said sarcosinate amido acids is conducted at a temperature from about 80°C to about 200°C, especially from about 120°C to about 200°C. The method herein employs a sarcosine salt, and preferably the carboxylic acid ester is a methyl or ethyl ester (R 1 = methyl or ethyl) having substituent R as C5- c 24* In order to facilitate mixing of the reactants and minimize reaction time, it is preferred to (a) conduct the reaction in an alcohol solvent which has a boiling point of at least 100°C; and/or (b) use a basic catalyst such as a sodium or potassium alkoxide. The reaction proceeds in about 85% yield with a molar ratio of fatty methyl ester reactant to sarcosine salt reactant to basic catalyst of about 1 1 0 05-0 2 All percentages, ratios and proportions herein are on a mole basis, unless otherwise specified. All documents cited are incorporated herein by reference DETAILED DESCRIPTION OF THE INVENTION The reaction sequence for the synthesis of the sarcosinate amido acids is shown below. The reaction sequence as illustrated employs oleic methyl ester and sarcosine sodium salt, but this is only by way of illustration and not limitation, as will be seen hereinafter. Sequence 1 CH 3 O NaO e catalyst O CH, O Oleic Methyl Ester Sodium Sarcosine Oleoyl Sarcosinate The following is by way of illustration, and not limitation, of conditions, equipment and the like, useful in the instant process. Reaction Process: The carboxylic acid ester reactant can be selected from alkyl esters (preferably methyl or ethyl) of straight chain aliphatic, branched chain aliphatic, saturated or unsaturated, aromatic, heteroaromatic, ethercarboxylic and cycloaliphatic carboxylic acids Nonlimiting examples include methyl or ethyl esters of the following carboxylic acids' acetic, propionic, butyric, caprylic, caproic, nonanoic, 3,5,5-trimethylhexanoic, decanoic, lauric, myristic, palmitic, stearic, oleic, linoleic, behenic, 2-methyl-undecanoic, 2-butyl-octanoic, 2-ethyl-hexanoic, alkyl- and alkenylsuccinic, adipic, cyclohexyl, C ^ JEO^CO-H, benzoic, chloro-benzoic, nitrobenzoic, naphthenic, abietic, nicotinic, 2-pyridine-carboxylic, terephthalic, phthalic, and mixtures thereof. Methyl ester mixtures derived from high oleic content natural oils (preferably having at least about 60%, more preferably at least about 75%, and most preferably at least about 90% oleic content) are especially preferred as starting materials for amido acid surfactants. The sarcosine salt reactant can be, for example, the sodium or potassium salts of sarcosine. The sodium salt of sarcosine can be generated either by neutralizing the amino acid with a sodium hydroxide solution and then drying or by neutralizing with sodium methoxide (convenient for lab preparations since it does not introduce water). The reaction conditions in the present invention process may be as follows Any air in the system during the amidation step causes darkening of the reaction mixture. Consequently, an inert gas (nitrogen is convenient) is sparged through the reaction mixture during this step. Inert gases such as argon, or the like, can also be used The objective is to provide a nonoxidizing reaction system in order to minimize the formation of colored contaminants. An alcohol can serve as the solvent for the amide formation step. It is preferred that the alcohol boiling point be less than 200°C, if it must be removed from the amido acid. 1-Butanol is a preferred solvent, since it can easily be removed from the product by distillation and for economical reasons be easily recycled In the amidation step, introduction of water from the reactants or solvents drastically reduces the yield. Alkoxide base is converted to hydroxide which hydrolyzes the fatty methyl ester to fatty acid salt. Alkoxide or stronger base is necessary for amidation to proceed and its consumption causes amidation to stop Introduction of sodium or potassium hydroxide also limits yield because of ester hydrolysis To avoid this problem, the reactants and solvents should be as moisture- free as possible. The sarcosine salt can be dried either by heating to ~100°C under vacuum or by using a solvent (e.g., 1-butanol) to azeotropically remove water Alternatively, the sarcosine salt can be dispersed in the fatty methyl ester and heated to ~140°C at ambient pressure for 0.5 hr. Excess hydroxide in the sarcosine salt can be neutralized with acid prior to drying or if it is at a low level, acid can be added to the amidation reaction mixture prior to adding the fatty ester and alkoxide base. The amidation reaction mixture can be very viscous and the use of alcohol solvents can reduce the viscosity. Various alcohols boiling above 100°C are suitable including 1-propanol, 1- and iso-butanol, 1-hexanol, 2-ethylhexanol, octanol, propylene and ethylene glycol. Fatty acid salts or amido acid salts also help solubilize the reactants. In the case of oleoyl sarcosinate sodium salt, no solvent is necessary if the reaction is performed at 160-200°C. This is because the oleoyl sarcosinate sodium salt is fluid at these temperatures and is capable of solubilizing the reactants It is generally useful to take part of a previous reaction mixture (heel) to solubilize the reactants of the next amidation reaction A base with a basicity equal to or greater than alkoxides is necessary to catalyze amidation. Various alkoxides are suitable such as sodium methoxide, sodium ethoxide, sodium t-butoxide, and potassium t-butoxide. Bases capable of forming alkoxides from alcohols are also suitable including sodium metal, potassium metal, sodium and potassium hydride. Sodium methoxide is preferred for economic reasons. The order of reagent addition is also important for minimizing fatty acid salt production. It is preferred to first disperse the sarcosine salt in the solvent with the fatty methyl ester or heel of the previous reaction and then heat to the desired reaction temperature. This helps drive off any water which may be present in the sarcosine salt or fatty methyl ester. The basic catalyst is added last. Reaction temperatures in the amidation step will typically be above about 80°C and below about 200°C and are preferably in the range from about 1 10°C to about 200°C. For low boiling carboxylic acid esters such as ethyl acetate, it may be appropriate to use a pressure vessel in order to achieve the desired reaction temperature. Reaction times can vary, of course, depending on the reactant volumes being employed. However, as a general rule for reactions in the 100 mis size range, a reaction time in the range from about 0.5 hours to about 4 hours is sufficient. During the amidation step, the alcohol originating from the carboxylic acid ester (typically methanol) is distilled from the reaction. In order to accelerate the reaction, some of the alcohol solvent (typically butanol) may also be removed so long as the reaction mixture is still easily stirred. If the reaction is conducted without solvent, foaming caused by methanol evaporation can be a problem. Addition of common defoamers such as Dow Corning Silicone 200 can alleviate this. Antioxidants commonly used in foods and plastics industries may also be added to the reaction mixture to improve color and/or odor of the sarcosinate product, such as BHA, BHT, Tenox, and/or Irganox antioxidants. Metal sequestrants may also be useful in the present process for similar benefits, and include for example Dequest 2066. Reaction stoichiometry in the amidation step employs a molar ratio of sarcosine salt reactant to carboxylic acid ester to basic catalyst of about 1 : 1 :0.05-0.2. Sarcosine remaining in the reaction mixture can be converted to an amide by addition of maleic or acetic anhydride to the mixture. Minimizing the sarcosine content minimizes any potential for nitrosamine formation. After the amidation step, the sarcosinate amido acid salt can be neutralized to the sarcosinate amido acid and the alcohol solvent removed. A variety of acids (e.g., sulfuric, formic acids) can be used to neutralize the alcohol solution of the amido acid salt so long as the salt of the neutralization acid is sparingly soluble in the alcohol solvent For example, acetic acid is not as preferred as formic acid because sodium acetate is more soluble than sodium formate in methanol/butanol Formic acid is convenient if 1 -butanol is the reaction solvent Sodium formate is sparingly soluble in 1 -butanol and precipitates Amido acid is soluble in the butanol Typically a molar ratio of acid to amido acid salt of about 1 1 is used Finally, butanol is removed from the amido acid by distillation and can be recycled GC Analysis Method This method is applicable to the determination of the relative content of sarcosine, fatty acids, fatty acid methyl esters, and alkanoyl sarcosinate in reaction samples The components listed above are separated, after silylation, by temperature programmed GC on a 15m DB1 column A cool on-column injector is used and detection is by FID Quantitation is performed using a C 12 fatty acid internal standard The materials containing active hydrogens are derivatized with a 3 1 9 1 mixture of HMDS TMCS Pyridine BSA Chemicals- Pyridine, low water J T Baker TMCS, Trimethylchlorosilane Pierce HMDS, Hexamethyldisilizane Pierce BSA, N,O-bis (trimethylsilyl)trifluoroacetamide Pierce Laurie Acid, 99.5% Aldrich Equipment Hewlett Packard 5890 GC Hewlett Packard On-column injection flame ionization detector Column 15m, DB-1, J&VV Scientific 0 25mm ID, 0 25um film Retention Gap 1 m, 0 53 mm ID Restek Procedure 1 Internal Standard/Derivatization solution Preparation Prepare a 1400 ppm solution of the lauric acid in pyridine Combine 7 parts of this solution with 2 parts of additional pyridine, 3 parts HMDS, 1 part TMCS, and 3 parts BSA The resulting solution will provide the required 3 1 9 ] derivatization solution with 700 ppm of lauric acid internal standard This internal standard/ derivatization solution will be used in the preparation of all calibration standards and unknowns This solution should be made fresh daily Calibration Standards Preparation Prepare standards for each component which bracket the levels expected in the unknown samples Each sample should also be made containing 700 ppm of the lauric acid internal standard For example, to prepare a 900 ppm calibration standard for oleic acid. Weigh 4 5 mg of oleic acid into a 5 mL volumetric flask Next, dilute to mark with the combined internal standard/derivatization solution Mix well Transfer ca 1 mL of the sample to a GC vial Cap and place vial in heated block at 80° C for 40 minutes The sample is now ready to be GC'ed Unknown Sample Preparation Weigh 5 0 mg of sample into a 5 mL volumetric flask Dilute to mark with combined internal standard/derivatization solution Mix well and transfer ca 1 mL to a GC vial Cap and heat for 40 minutes at 80° C The sample is now ready to be GC'ed Instrument Settings Inlet Temperature 60° C Detector Temperature 340° C Level Rate Temp Time Initial 60° C 1 0 min Level 1 10° C/min 160° C 0 0 min Level 2 7° C/min 325 0 C 10 0 min Level 3 30° C/min 340° C 10 0 min Total Run Time 55.07 minutes 5 Approximate Retention Times C18 0 Fatty Acid 24 0 C14 Sarcosinate 26 2 C15 Sarcosinate 26 9 C16 1 Sarcosinate 28 3 C16 0 Sarcosinate 28 6 C17 Sarcosinate 29.6 C18 1 Sarcosinate 30 6 C18 0 Sarcosinate 30 9 C20 1 Sarcosinate 32 5 C20 0 Sarcosinate 32 8 6 Calculation of Rfs for Calibration After chromatographing each calibration standard, compile the areas for the compound and internal standard for each run Calculate the Rf as follows Rf = Area Compound * Cone Internal Standard Cone Compound Area Internal Standard Concentration is in units of ppm Calculate an average Rf for each compound using the multiple calibrations standards which were run 7 Calculation of Weight Percent After running the unknown sample, determine the peak areas for each component plus the internal standard Using the Rf for a given component, calculate the weight percent as follows First, calculate the cone of the component in the injected sample Cone Compound = Area Compound * Cone Internal Standard Rf Area Internal Standard Finally, calculate the weight percent Weight Percent Compound = (Cone Compound, ppm) * Vg_* 1 00 o /o c Where, V c = Volume of flask in which unknown sample was prepared (in L) W c = Weight of sample weighed into flask (in mg) EXAMPLE I Synthesis of Oleoyl Amide of Sarcosine Sodium Salt - A 500 mL, 3 -neck, round bottom flask is fitted with thermometer, Dean-Stark trap with condenser, mechanical stirring, and a purge tube through which nitrogen is passed through the reaction mixture The reaction vessel is charged with sarcosine (8 0 g, 0 09 mol), sodium methoxide 25% in methanol (23.3 g, 0. 108 mol), and methanol (80 mL). The reaction is refluxed 15 min to neutralize the sarcosine and then methanol is distilled off using the Dean-Stark trap. The reaction mixture is then heated to 160°C and methyl oleate 70% (40.0 g, 0.094 mol) is added. Reaction is kept at 180°C for 1 .0 hr during which methanol is collected in the Dean-Stark trap. The reaction is allowed to cool and the desired product (49.8 g) is obtained. EXAMPLE II Synthesis of Oleoyl Amide of Sarcosine Sodium Salt - A 100 mL, 3 -neck, round bottom flask is fitted with thermometer, Dean-Stark trap with condenser, mechanical stirring, and a gas inlet adapter through which nitrogen is passed over the reaction mixture. The reaction vessel is charged with sarcosine (1.5 g, 0.0165 mol), sodium methoxide 25% in methanol (3.26 g, 0.0157 mol), and methanol (20 mL). The reaction is refluxed 15 min to neutralize the sarcosine and then methyl oleate (99%) (4.94 g, 0.0165 mol) is added. Any water in the reaction mixture is removed by heating to 170°C for 1 hr and the methanol is collected using the Dean-Stark trap. The reaction is initiated by the addition of sodium methoxide 25% in methanol (0.55 g, 0.0026 mol). Reaction is kept at 170°C for 2.5 hr during which methanol is collected in the Dean-Stark trap. Analysis of the reaction mixture by GC Method gives 79.6% sodium oleoyl sarcosinate, 10.3% sodium oleate, and 6.3% sarcosine. Then acetic anhydride (0.41 g, 0.004 mol) is added to scavenge the remaining sarcosine. Analysis of the reaction mixture by GC Method gives 84.1% sodium oleoyl sarcosinate, 11.1% sodium oleate, and 0% sarcosine. EXAMPLE III Synthesis of Oleoyl Amide of Sarcosine Sodium Salt - A 100 mL, 3-neck, round bottom flask is fitted with thermometer, Dean-Stark trap with condenser, mechanical stirring, and a gas inlet adapter through which nitrogen is passed over the reaction mixture. The reaction vessel is charged with sarcosine (3.0 g, 0.033 mol), sodium methoxide 25% in methanol (6.86 g, 0.033 mol), and methanol (35 mL). The reaction is refluxed 15 min to neutralize the sarcosine and then most of the methanol is removed by distillation. Then methyl oleate (99%) (9.88 g, 0.033 mol) is added and the reaction mixture is heated to 150°C. Then 1 -butanol (40 mL) is added dropwise over 0.5 hr to remove by azeotropic distillation any water present in the reactants. Then the reaction is initiated by the addition of sodium methoxide 25% in methanol (1.37 g, 0.0066 mol) over 10 min. Reaction is kept at 150°C for 1.5 hr during which methanol/butanol is collected in the Dean-Stark trap During the course of the reaction, additional 1-butanol (8 mL) is added. Analysis of the reaction mixture by GC Method gives 86 9% sodium oleoyl sarcosinate, 7 0% sodium oleate, and 2 4% sarcosine Example IV Synthesis of High-Oleic Natural Oil-Derived Amides of Sarcosine Sodium Salt - A 2L, 3-neck, round bottom flask is fitted with thermometer, Dean-Stark trap with condenser, mechanical stirring, and a gas inlet adapter through which nitrogen is passed over the reaction mixture The reaction vessel is charged with sarcosine 98% (33.4 g, 0 368 mol), sodium methoxide 25% in methanol (75 5 g, 0 35 mol), and methanol (400 mL). The reaction is refluxed 15 min to neutralize the sarcosine and then methyl ester derived from high-oleic natural oil ( 120 0 g, 0 405 mol) is added Any water in the reaction mixture is removed by heating to 170°C for 1 hr and the methanol is collected using the Dean-Stark trap. The reaction is initiated by the addition of sodium methoxide 25% in methanol (1 1 9 g, 0.055 mol) Reaction is kept at 170°C for 2.5 hr during which methanol is collected in the Dean-Stark trap The reaction is allowed to cool to 70°C and methanol (250 mL) is added to the reaction mixture in order to transfer it out of the flask Ethyl acetate (250 mL) is added to the methanol solution and this solution is kept at 40°C overnight in order to precipitate fatty acid salts. The solution is then filtered and the filtrate evaporated to give an orange-brown product ( 127g) Analysis of the reaction mixture by GC Method gives 72.3% sodium oleoyl sarcosinate, 5 8% sodium oleate, and 3 0% sarcosine.

Claims: What is Claimed is: 1. A method for preparing sarcosinate amido acids and salts thereof of the formula O CH 3 R-C-N-CH2-CO2M (IA) wherein R is a C-, or higher hydrocarbyl substituent, and M is a cationic moiety selected from alkali metal salts and hydrogen, comprising the steps of: (a) reacting under anhydrous conditions, in the presence of a base catalyst with basicity equal to or greater than alkoxide catalyst, a carboxylic acid ester of the formula O 11 R-C-OR1 with a sarcosine amino acid salt of the structure CH 3 H-N-CH 2 -Cθ 2 M wherein R is as described before, R is a C , or higher hydrocarbyl substituent, and M is an alkali metal salt; and (b) optionally, neutralizing the sarcosinate amido acid salt formed by step (a) to form the sarcosinate amido acid, whereby M is hydrogen in formula IA. 2. The method according to Claim 1 wherein R is Cg-C24 and R 1 is methyl or ethyl. 3. The method according to either of Claims 1 or 2 wherein the the reaction step (a) is catalyzed by alkoxide base. 4. The method according to any of Claims 1-3 wherein the carboxylic acid ester is an oleic ester. 5. A method for preparing oleoyl sarcosinate acids and alkali metal salts thereof comprising the steps of: (a) reacting under anhydrous conditions, in the presence of an alkoxide base catalyst, an oleic ester with a sarcosine amino acid salt of the structure CH3 H— N-CH 2 -CO2M wherein M is an alkali metal salt; and (b) optionally, neutralizing the oleoyl sarcosinate amido acid salt formed by step (a) to form the oleoyl sarcosinate amido acid. 6. The method according to Claim 5 wherein the oleic ester is selected from methyl ester, ethyl ester, and mixtures thereof, and the alkoxide base catalyst is selected from sodium alkoxide, potassium alkoxide, and mixtures thereof. 7. The method according to any of Claims 1-6 wherein the base catalyst is an alkoxide base catalyst selected from the group consisting of sodium methoxide, sodium ethoxide, sodium t-butoxide, potassium t-butoxide, and mixtures thereof. 8. The method according to any of Claims 1-7 wherein, prior to step (a) addition of base catalyst, any hydroxide present is neutralized with acid and then the reaction mixture dried. 9. The method according to Claim 1 1 wherein the reaction step (a) utilizes an alcohol solvent having a boiling point above 100°C. 10. The method according to any of Claims 1-9 wherein the reaction step (a) utilizes an alcohol solvent selected from the group consisting of 1-propanol, 1 - and iso-butanol, 1-hexanol, 2-ethylhexanol, octanol, propylene and ethylene glycol, and mixtures thereof. 1 1. The method according to any of Claims 1-10 wherein the alkoxide base catalyst is sodium methoxide, and the sarcosine amino acid salt is selected from the group consisting of sodium salt, potassium salt, and mixtures thereof 12. A method for preparing oleoyl sarcosinate acids and alkali metal salts thereof comprising the steps of: (a) reacting under anhydrous conditions, in the presence of sodium methoxide base catalyst, an oleic methyl ester with a sarcosine amino acid sodium or potassium salt, or mixtures thereof; and (b) optionally, neutralizing the oleoyl sarcosinate amido acid salt formed by step (a) to form the oleoyl sarcosinate amido acid. 13. The method according to any of Claims 1-12 wherein the molar ratio of oleic ester reactant to sarcosine salt reactant to alkoxide base catalyst is 1 : 1 :0.05-0.2.

Inventors: DUPONT JEFFREY SCOTT, HEINZMAN STEPHEN WAYNE, DUPONT, JEFFREY, SCOTT, HEINZMAN, STEPHEN, WAYNE
Applicants: PROCTER & GAMBLE, THE PROCTER & GAMBLE COMPANY
Application year: 1994
Main classification: C07C231
IPC codes: C07C231, C07C233, C11D1